This invention relates to the art of treating metals, metal alloys and metal oxides, and more particularly to a new and improved method for enhancing the electrical conductivity of metals, metal alloys and metal oxides.
One area of use of the present invention is in the manufacturing of electrodes for capacitors, batteries and the like, although the principles of the present invention can be variously applied. Metals and metal alloys have a native oxide present on the surface. This is an insulating layer and hence if the material is to be used as a substrate for an electrode, the oxide has to be removed or made electrically conductive.
If the oxide is removed by chemical treatment, such as by etching with an acid or electrolytic etching to expose the underlying metal, special steps must be taken in order to complete the electrical contacts before the native oxide can be regenerated and interfere with the electrical contacts. Such measures require special apparatus and extremely careful handling of the materials, all of which adds cost to the fabricating of electrical devices incorporating these materials to which electrical contact must be made. Another approach involves removing the oxide layer and plating the bare substrate metal with an expensive noble metal, such as silver, gold, or alloys of silver, gold and platinum, or the formation of an electrically conducting compound on the bare substrate surface. The materials employed are expensive and the steps required to plate the substrate are costly and time consuming. In addition, the metal plating or electrically conducting compound must be disposed on the substrate as a continuous film for maximum performance. Therefore, the plating or compound formation typically is carried out after the substrate metal is formed into its final shape for the electrical device in which it is incorporated in order to avoid damage to the coating. This, in turn, adds to the cost and complexity of the manufacturing process.
U.S. Pat. No. 5,098,485 issued Mar. 24, 1992 to David A. Evans proposes a solution to the oxide problem by altering the native oxide from an electrically insulating to an electrically conducting condition without removal of the native oxide layer to expose the underlying metal or alloy. A solution containing ions of an electrical material is applied to the native oxide layer, and then the substrate, oxide and applied ions are heated to an elevated temperature for a time sufficient to incorporate the ions into the oxide layer to change it from an electrical insulator to an electrical conductor.
It would therefore, be highly desirable to provide a new and improved method for enhancing the electrical conductivity of metals, metal alloys and metal oxides which does not require additional heat treatment, which provides control over the density and depth of the material introduced to the treated surface, which can be performed in a manner preventing substrate degradation and deformation, and which improves the quality of the treated surface.
The present invention provides a method for improving the electrical conductivity of a substrate of metal, metal alloy or metal oxide comprising depositing a small or minor amount of metal or metals from Group VIIIA metals (Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt) or from Group IA metals (Cu, Ag, Au) on a substrate of metal, metal alloys and/or metal oxide from Group IVA metals (Ti, Zr, Hf), Group VA metals (V, Nb, Ta), Group VIA metals (Cr, Mo, W) and Al, Mn, Ni and Cu and then directing a high energy beam onto the substrate to cause an intermixing of the deposited material with the native oxide of the substrate metal or metal alloy. The native oxide layer is changed from electrically insulating to electrically conductive. The step of depositing can be carried out, for example, by ion beam assisted deposition, electron beam deposition, chemical vapor deposition, physical vapor deposition, plasma assisted, low pressure plasma and plasma spray deposition and the like. The high energy beam can be an ion beam from a high energy ion source or it can be a laser beam. The deposition may be performed on either treated or untreated substrate.
The method of the present invention advantageously does not require additional heat treatment and provides control over the density and depth of the material mixed into the treated surface thereby not affecting the bulk of the material. The method can be performed at a temperature sufficiently low so as to prevent substrate degradation and deformation. It is believed that the quality of the treated surface is improved by the method of the present invention. Another advantage is that using a substrate treated by the method of the present invention will allow the surface thereof to be treated to passivate it from chemical reaction while still providing adequate electrical conductivity. Stainless steels having native insulating oxide layers also can be treated by the method of the present invention to provide an electrically conductive oxide layer.
A substrate treated by the method of the present invention is ready for further processing in the manufacture of an electrode for use in capacitors, batteries and the like. Typically, in the case of a capacitor, an appropriate electrode material is deposited on the substrate treated surface by techniques well-known to those skilled in the art. Examples of electrode materials are redox pseudo capacitance materials such as, but not limited to, oxides and mixed oxides of ruthenium, iridium, manganese, nickel, cobalt, tungsten, niobium, iron, molybdenum, double layer materials or under potential deposition systems such as palladium, platinum, lead dioxide or electro-active conducting polymers such as polyaniline, polypyrole and polythiophene.
The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent upon a reading of the ensuing detailed description together with the included drawing wherein: